Safety interlock for fluid-operated, load-handling apparatus

ABSTRACT

Load-handling apparatus is provided which includes a safety interlock to prevent the disengagement of a load when the apparatus is in an operative condition to balance or raise the load. The apparatus includes a fluid-operated hoist and a fluidoperated, load-engaging unit. A blocking valve is provided which is responsive to pressure of fluid for the hoist, which valve presents the load-engaging unit from disengaging the load when the pressure is at least equal to a predetermined value which is usually sufficient to at least balance the load.

United States Patent 1 Stone [451 May 22, 1973 [54] SAFETY INTERLOCK FOR FLUID- OPERATED, LOAD-HANDLING APPARATUS [7 5 l nvento r z harles' W. Stone, Garden City,

Mich.

[73] Assignee: D. W. ZimmermanMfg., Inc., Madi son Heights, Mich.

[22] Filed: Mil. 31, 1971 [21] Appl. No.: 129,863

[52] US. Cl. ..214/658, 294/64 R [5 l Int. C1 .1366! 1/02 [58] Field Of Search ..214/658, 64 R [56] References Cited 1 v UNITED STATES PATENTS 2,732,083 1/1956 Smith ..2l4/658 2,911,793 11/1959 Arnot ..214/653 X 3,382,771 5/1968 Nutter ..214/653 X 2,665,013 1/1954 Socke ..294/64 R X Primary Examiner-Robert G. Sheridan Assistant ExaminerGeorge F. Abraham Attorney-Allen D. Gutchess [57] ABSTRACT Load-handling apparatus is provided which includes a "safety interlock to prevent the disengagement of a mined value which is usually sufficient to at least balance the load.

5 Claims, 5 Drawing Figures Patented May 22, 1973 3,734,325

3 Sheets-Sheet 2 FIG. 2

FIG. 5

I 40 q- INVENTOR.

[42 q CH RLEs W- fibms:

ww w t SAFETY INTERLOCK FOR FLUID-OPERATED, LOAD-HANDLING APPARATUS This invention relates to fluid-operated, loadhandling apparatus with safety interlock means to prevent disengagement of a load when the apparatus is under sufficient pressure to balance or raise the load.

Fluid-operated hoists of various types, such as shown in U.S. Pat. No. 3,260,508, are now in common use for manipulating loads. Hoists particularly of the type shown in the aforesaid patent can be used at different fluid pressures to raise or lower loads or to balance them so that they can be manipulated by an operator with little effort. Such hoists are frequently used with fluid-operated, load-engaging units which are operated by fluid pressure to engage and disengage the loads. Fluid-operated vacuum cups, as shown in U.S. Pat. No. 3,423,119, are examples of such units.

Heretofore, it has been possible with such loadhandling apparatus for an operator to inadvertently release the load when the hoist is under fluid pressure sufficient to balance or raise the load. When this has occurred, the hoist pressure causes the load-engaging unit to quickly rise, the weight no longer being carried, with the result that the unit may strike the operator or others, causing injury. Also, if the load is above the floor or other support at the time of release, it will fall and may injure the operator or others, or damage the load or whatever it drops upon.

Heretofore, mechanical means have been employed to a limited extent with a fluid-operated hoist to prevent the load-engaging unit from quickly rising or flying up if the load carried thereby is released when the hoist is under sufficient fluid pressure. An example of such means can be found in U.S. Pat. No. 3,276,747. Such mechanical means physically stops the cable drum of the hoist when its speed of rotation is excessive. However, this also stops the hoist hook completely and the operator loses control over it. When the operator is manipulating a load, the mechanical means also may stop the drum if the operator raises it too fast. Therefore, the operator often must manipulate the load more slowly than be otherwise could. Further, if the mechanical means engages and stops the cable drum when the operator is lifting a load off a conveyor, by way of example, dire consequences can result as the load continues to be moved away by the conveyor with the cable connected thereto and with the drum and cable stopped and prevented from movement by the mechanical means. Also, means of this type does not prevent the operator from inadvertently releasing the load and causing damage.

The present invention provides fluid-operated, loadhandling apparatus including a safety interlock which prevents the load from being disengaged when the hoist is under a predetermined pressure, usually a pressure sufficient to at least balance or to raise the load. In a preferred form, the safety interlock includes a pressure-responsive valve which is effective to prevent fluid pressure from being transmitted to the load-engaging unit or to block the release of fluid under pressure from the unit, depending upon the type of unit, and thereby prevent disengagement of the load except when the fluid pressure in the hoist is at a low value. Under the latter condition, if the load is released, the loadengaging unit will not quickly rise and, with the hoist under low pressure, the load engaged by the unit will most likely be supported by the floor or other supporting surface so that it cannot drop.

It is, therefore, a principal object of the invention to provide fluid-operated, load-handling apparatus with a safety interlock to prevent injury to the operator or to other personnel and to prevent damage to the load or any support thereunder.

Another object of the invention is to provide fluidoperated, load-handling apparatus with safety interlock means to prevent the load from being disengaged when the apparatus is under a predetermined pressure.

Still another object of the invention is to provide a fluid-operated hoist with a fluid-operated, loadengaging unit and a safety interlock to enable the unit to disengage the load only when the hoist controller is in a predetermined position and the hoist pressure is not enough to balance or raise the load.

Other objects and advantages of the invention will be apparent from the following detailed discussion of preferred embodiments thereof, reference being made to the accompanying drawings, in which:

FIG. 1 is a somewhat schematic overall view in perspective, with parts broken away, of a fluid-operated hoist and a fluid-operated, load-engaging unit with a safety interlock according to the invention;

FIG. 2 is a diagrammatic view of fluid controls used with the apparatus of FIG. 1;

FIG. 3 is a view in cross section of a safety interlock blocking valve according to the invention;

FIG. 4 is a somewhat schematic view in perspective of a fluid-operated hoist and a modified fluid-operated, load-engaging unit with a safety interlock according to the invention; and

FIG. 5 is a diagrammatic view of fluid controls used with the apparatus of FIG. 4.

Referring particularly to FIG. 1, a pneumaticallyoperated hoist with which the invention can be used is indicated at 10. This hoist can be of the type shown in U.S. Pat. No. 3,260,508, although other pneumaticallyoperated hoists can also be used advantageously with the invention. The hoist l0 basically includes a chamber 12 to which fluid, usually air, under pressure is supplied, a piston 14, and a cable drum 16 carrying a flexible cable or load-carrying member 18. When fluid under sufficient pressure is supplied to the chamber 12, it forces the piston 14 toward the opposite end of the hoist 10 and moves the cable drum 16 in the same direction. The drum 16 is supported on a ball screw assembly (not shown), causing the drum to rotate as it moves longitudinally therealong in the hoist 10. When the piston moves toward the end of the hoist opposite the chamber, the drum 16 rotates in a manner to raise the cable 18. When the pressure in the chamber 12 is sufficiently low, the weight of a load carried on the cable 18 will cause the drum 16 to rotate in a manner to lower the cable and to move the piston 14 and the drum 16 toward the chamber 12 of the hoist, reducing the volume of the chamber. Hence, when the fluid pressure in the hoist 10 is sufficient, it will raise the cable 18 and the load; when the pressure is sufficiently low, the load on the cable 18 will be lowered. Further, when the pressure in the chamber 12 is adjusted to a predetermined value to balance the weight of the load carried by the cable 18, this enables an operator to manipulate the load up and down as if it had little weight.

The air pressure for the chamber 12 is controlled through a regulator control 20 which is preferably of the pilot air controlled type, as shown in U.S. Pat. No. 3,457,837.

The cable 18 is connected by a hook 22 to a fluidoperated, load-engaging unit indicated at 24 which can be of the type disclosed more fully in U.S. Pat. No. 3,423,119. The unit 24 basically includes a frame 26 to which is pivoted a hanger 28 carried by the hook 22. Two fluid-operated, load-engaging vacuum cups 30 and 32 are mounted on central hubs or supporting blocks 34 and 36 which, in turn, are fastened to structural members of the frame 26. Vacuum is established in the cups 30 and 32 to enable them to securely engage the load. Means are also provided to supply air under pressure to the vacuum cups to blow off the cups and enable the unit 24 to quickly disengage a load, when desired. A three-position control valve 38 controls air pressure to the hoist chamber 12 through the regulator control 20 and is also mounted on the frame 26, having a handle 39 to aid in manipulating the unit 24. This control valve also can be similar to that shown in the aforementioned U.S. Pat. No. 3,260,508. A valve handle 40 mounted on the opposite end of the frame 26 is used to control the vacuum in the cups and the blowoff air supplied to the vacuum cups 30 and 32 to disengage the load. The handles 39 and 40 are also used by the operator to manipulate the unit 24 and the load carried thereby.

The operation of the hoist l and the load-handling unit 24 will be discussed more fully in connection with the diagrammatic view of the controls in FIG. 2. Fluid, such as air, is supplied to the regulator control 20 through a suitable supply line 42. Part of this air is taken directly from the regulator control 20 through a depending line 44 to a line 46 which directs the air through a venturi 48, with the air being dissipated through a silencer 50. A vacuum line 52 is connected to the throat of the venturi 48 so that a vacuum is established in the line 52 when air is supplied through the venturi 48, in a manner known in the art. The vacuum line 52 is connected to the vacuum cups 30 and 32 by branch lines 54 and 56 communicating with the cups through the supporting blocks 34 and 36. Check valves can be located in the branch lines 54 and 56 to prevent vacuum established in the cups 30 and 32 from being lost in the event of failure of the air supplied through the lines 44 and 46. This is also more fully discussed in the aforementioned U.S. Pat. No. 3,423,]19.

A three-way, push-button valve 58, associated with the valve handle 40, is located between the lines 44 and 46. A line 60 also connects the valve 58 with a fluidresponsive blocking valve 62 embodying the invention, which valve can also be mounted on the frame 26. A blow-off line 64 is connected to the blocking valve 62 and terminates in branch lines 66 and 68 communicating with the vacuum cups 30 and 32 through the supporting blocks 34 and 36. When the blocking valve 62 is open and the push button of the valve 58 is pressed to open it, air is supplied from the line 44 through the valve 58, the line 60, the valve 62, the line 64, and the branch lines 66 and 68 to the supporting blocks 34 and 36. This air enters the vacuum cups 30 and 32 and blows off or quickly disengages the vacuum cups 30 and 32 from the load. When the push button of the valve 58 is pressed, it simultaneously shuts off the air through the line 46 and the venturi 48. Otherwise, air continuously flows through the valve 58 to the venturi 48.

The manually-operated control valve 38 has three positions, as schematically shown in FIG. 2, and is connected with the regulator control 20 through a line 70. This control 20, shown schematically, includes a main regulator 72 which controls the pressure of the air supplied through the line 42 to the chamber 12 and also includes a pilot air-controlled regulator 74 which, in turn, controls the main regulator. The pilot aircontrolled regulator 74 and the line '70 are connected to a pilot air chamber 76 of the main regulator 72 to control the pressure therein, which, in turn, controls the output pressure of the main regulator. The control valve 38 has a central, blocked position indicated at A, a partially vented position indicated at B, and a more fully vented position indicated at C. When the valve 38 is in the central, blocked position A, no air is vented from the line and the chamber 76 and maximum pressure is thus acting upon the main regulator 72 in the control 20 to supply air under maximum pressure to the chamber 12. This pressure is sufficient to expand the chamber 12 and drive the piston 14 toward the opposite end of the hoist 10, thereby turning the drum 16 in a manner to raise the cable 18 and the load carried by the load-engaging unit 24. When the valve 38 is in the partially vented position B, somewhat lower pressure is acting upon the main regulator 72 in the control 20, with the vent preferably adjusted such that the pressure in the hoist chamber 12 will balance the load. The piston 14 will then not move in either direction unless the load is pushed down or up by the operator. Under this balanced condition, the operator can raise or lower the load as if it weighed only a few pounds. When the control valve 38 is in the third, more fully vented position C, even lower pressure acts upon the regulator 72 in the control 20 and air under lower pressure is supplied to the hoist chamber 12. The weight of the load then causes the drum 16 and the piston 14 to move toward the chamber 12 and the load is lowered until it reaches a supporting surface or floor, if not already supported. This lower pressure preferably is just sufficient to balance the unit 24 without a load.

When the valve 38 is in the blocked position A and air under maximum pressure is supplied to the chamber 12, the load carried by the load-engaging unit 24 will rise until the piston 14 moves to the opposite end of the hoist 10 or until the position of the control valve 38 is changed. During this condition, if the operator should inadvertently open the valve 58 of the handle 40 to blow off the vacuum cups 30 and 32, the load carried thereby will drop onto the supporting surface, either damaging the load or the surface or any other object it hits, including the operator. At the same time, the hook 22 and the unit 24, still being under the influence of the maximum pressure in the chamber 12, will rise rapidly or fly upwardly, frequently hitting the operator or others in the vicinity and, again, causing possible serious injury.

When the control handle 38 is in the partially vented position B to balance the load and the unit 24, if the valve 58 is opened to cause the vacuum cups to blow off and disengage the load, the load again will drop, if it is not then being supported, and can cause damage or injury. The book 22 and the load-engaging unit 24 will fly upwardly, although not quite as violently as when the control handle 38 is in the blocked position A, and still can cause injury.

The load is usually lowered to the supporting surface when the control valve 38 is in the partially vented position B, after which time the control handle is moved to the fully vented position C. Thus, the load is on or very close to a supporting surface when the control 38 is moved to the fully vented position C. If the valve 58 is now opened and air is supplied to the vacuum cups 30 and 32, the disengaged load will be supported or at least will not drop to any extent to cause injury or damage. In the position, the pressure also is sufficiently low preferably to balance the hook 22 and the unit 24 so that they can be raised or lowered by the operator, the same as the load can be when the control handle 38 is in the partially vented position B. Thus, the hook and load-engaging unit cannot cause injury either if the load is disengaged when the valve 38 in the fully vented position C.

In the valve position C, the blocking valve 62 should be opened so that blow-off air can be supplied to the vacuum cups 30 and 32 when the valve 58 is opened to enable the load to be disengaged. However, when the control valve 38 is in the partially vented position B or the blocked position A, the blocking valve 62 should be closed to prevent the possibility of the vacuum cups being blown off and the unit 24 disengaged from the load even if the valve 58 is opened.

A suitable design for the blocking valve 62 is shown in FIG. 3. The valve 62 includes a valve body 78 having a central bore 80 in which is a sealing cylinder 82 having appropriately placed O-ring seals 84 to contain fluid or air passing therethrough. A spool valve 86 is located in a central passage 88 formed by the cylinder 82 and includes a sealing piston 90 at one end portion and an enlargement 92 to serve as a guide at the other end portion. A coil spring 94 is in engagement with the latter end portion and is adjustable through a threaded adjusting nut 96 and an adjusting screw 98. An inlet recess 100 receives the line 60 and an outlet recess 102 receives the blow-off line 64. These communicate with the central passage 86 through transverse openings 104 and 106. A bore 108 in an end ring 110 connects the passage 86 with an end recess 112 which receives a line 114. The line 114 connects an end of the passage 86 with the line 70, as shown in FIGS. 1 and 2.

When the pressure in the line 70 and, consequently, the pressure in the chamber 12, is at least equal to a predetermined value, the pressure transmitted through the passage 86 is sufficient. to overcome the force of the spring 94 and urge the spool valve 86 downwardly to block flow between the passages 60 and 64, and specifically between the transverse ports 104 and 106. The valve 62 is thus closed and blow-off air cannot be transmitted to the vacuum cups 30 and 32 even if the valve 58 of the handle member 40 is open.

The force of the spring 94 can be adjusted by the adjusting screw 98 to select the pressure which is sufficient to move the spool valve 86 to the closed position. Preferably the pressure is at least sufficient to balance the load engaged by the load-engaging unit 24 so that the load cannot be disengaged in such a condition, enabling the unit 24 to rapidly rise and cause injury. This pressure occurs when the control valve 38 is in the blocked and partially vented positions A and B. However, when the pressure is below the predetermined pressures in the line 70 and in the chamber 12, which are directly proportional to one another, the pressure transmitted to the passage 88 is sufficiently low that the spring 94 takes over and moves the spool valve 88 to the upper position, as shown in FIG. 3, thereby enabling flow between the lines 60 and 64. Consequently, when the valve 58 of the handle member 40 is open, the blow-off air can be transmitted through the line 44, the valve 58, the line 60, the blocking valve 62, the line 64, and the branch lines 66 and 68 to the vacuum cups 30 and 32 to enable the load to be quickly disengaged. At this time, the load will be on or close to a supporting surface so that it cannot fall and cause damage or injury. Also, the pressure in the chamber 12 is not sufficient to cause the hook 22, the cable 18, and the unit 24 to rise rapidly, which could otherwise cause injury.

Modified load-handling apparatus embodying the invention is shown in FIGS. 4 and 5. Here, the same hoist 10 can be used or other fluid-operated hoists can be advantageously used, with the fluid pressure again controlled by the regulator control 20. The flexible loadcarrying member or cable 18 is connected, in this instance, by a loop 116 to a modified fluid-operated, load-engaging unit indicated at 118. The unit 118 includes a frame 120 on which can be mounted the threeposition control valve 38 which is connected to the regulator control 20 by the line 70. Two fluid-operated, load-engaging levers 122 and 124, which can be substantially identical, are also on the frame 120. These levers include L-shaped members 126 and arms 128 integrally connected thereto and having intermediate ears 130 pivoted to supporting blocks 132 carried on the frame 120. The L-shaped members 126 are designed to fit under inwardly projecting portions of a load, being represented in this instance in dotted lines 134 as a transmission housing. Ends of the arms 128 are located side-by-side and are pivotally connected by a pin 136 to a clevis 138. The clevis is affixed to the upper end of a piston rod 140 connected to a piston 142 in a cylinder 144.

In operation, when the piston 142 is moved to the upper end of the cylinder 144, the adjacent ends of the arms 128 are raised to pivot the load-engaging levers 122 and 124 in a manner to move the L-shaped members 126 inwardly to a retracted position. Similarly, when the piston 142 is moved to the bottom of the cylinder 144, the arms 128 are lowered to cause the L- shaped members 126 to move outwardly to an extended position. When the load-engaging levers 122 and 124 are in the retracted position, the unit 118 can be lowered into the housing or load 134 or disengaged therefrom. At this time, fluid is supplied to the upper end of the cylinder 144 to cause the piston 142 to move downwardly and move the L-shaped members 126 to the extended position, in which instance the extremities of the members exceed the corresponding distance across the load. Consequently, when the unit 118 is raised, it will carry the load therewith off a supporting surface. For making a connection with the hoist, the unit 118 includes a bifurcated hanger 146 connected to the upper end of the cylinder 144 and also fastened to the frame 120.

The valve control 38 of FIGS. 4 and 5 can have the same positions as the counterpart of FIGS. 1 and 2. Hence, these positions are not shown in FIG. 5. When the valve 38 is in the blocked position A, again maximum pressure is supplied to the hoist chamber 12 and this pressure is sufficient to raise the load-engaging unit 118 and the cable 18. The load will then rise until the piston moves to the opposite end of the hoist or until the position of the control valve 38 is changed. When the control handle is in the partially vented position B, the load-engaging unit 118 and the load carried thereby will be balanced to enable the unit and the load to be manipulated as if they weighed only a fraction of their actual weight. In the fully vented position C of the control valve 38, the load and the load-engaging unit 118 will be lowered quickly to a supporting surface, if not already being supported.

Again, without the blocking valve 62, if air were supplied to the lower end of the cylinder 144 inadvertently, with the valve 38 in the first or second position, the piston 142 would rise and retract the L-shaped members 126, thereby disengaging the load. The load would then be dropped, causing damage to the load, surface, or personnel. The cable 18 and the unit 118 would also quickly rise, under the influence of the pressure in the chamber 12, causing possible injury to the operator or others. Consequently, as is true of the apparatus of FIGS. 1 and 2, it is desired to prevent the unit 118 from disengaging the load when the control handle is in the first or second, blocked or partially vented positions. However, it is desirable to have the unit be able to disengage the load when the valve is in the third, fully vented position.

In the first two positions of the control valve 38, the pressure in the hoist, as before, will be at least sufficient to balance the load whereas, in the third position, the pressure will be less than that required to balance or lift the load and preferably will be only sufficient to balance the load-engaging unit 118. Thus, a fluidresponsive interlock valve used with the apparatus of FIG. 4 should prevent disengagement of the loadengaging unit from the load in the first two positions of the control valve and should enable disengagement when the control valve is in the third position and the hoist is subjected to low fluid pressure.

Referring to FIG. 5, the operation of the apparatus of FIG. 4 will be more fully explained. The three-position control valve 38 is connected with the regulator through the line 74) and has the branch line 114 connected with the recess 112 (FIG. 3) of the blocking valve 62 (not shown in FIG. 4). In this instance, the branch line 44 supplies air to a four-way valve 148 (omitted from FIG. 4 for clarity of illustration) which controls the position of the piston 142 in the cylinder 144. When the valve 148 is in one position, it supplies air through a line 150, a regulator 152, and a line 154 to the blind end of the cylinder 144. At the same time, the valve 148 vents air from the rod end of the cylinder 144 through a line 156, the blocking valve 62, if open,

' and a line 1158. In a second position of the valve 148,

it supplies air through the line 158, the valve 62, if open, and the line rss to the rod end of the cylinder I44, venting air through the line 154, the regulator 152, and the line 150. In the first position of the valve 148, the piston 142 is moved to the rod end of the cylinder, the upper end in FIG. 4, and the members 126 are in the retracted position. In the second position of the valve 148, the piston 142 is moved to the blind end of the cylinder I44 and the members 126 are in the extended position, as shown in FIG. 4.

When the control valve 38 is in the blocked or partially vented position, the pressure in the hoist will be sufficient to raise or balance the load. In this instance, it is desired that the piston 142 remain at the blind end or engaged position in the cylinder 144. This is automatically accomplished by maintaining the valve 62 closed between the lines 156 and I58, which prevents the air in the rod end of the cylinder 144 from being vented, even if the valve 148 is moved to the disengaged position to supply air through the lines 150 and 154. The regulator 152 is used to reduce the pressure of the air supplied through the line 154 to the cylinder 144 so that this air cannot possibly override the air at the rod end of the cylinder, which is acting upon a reduced area of the piston, and cause undesired movement of the piston. When the control valve 38 is in the third, vented position, with the hoist under low pressure, the valve 62 will then open because the spring 94 (FIG. 3) will override the air pressure and move the spool valve 86 to the open position. The air in the rod end of the cylinder 144 can then be vented through the line 158 and the valve 148 to enable the piston 142 to move toward the rod end of the cylinder and retract the L-shaped members 126 to disengage the load.

Numerous modifications of the invention will be apparent from the above description and the drawings. By using different types of pressure-responsive valves, different positions of the valves and operation thereof will be employed. Also, many types of fluid-operated hoists and load-engaging units can be used with the invention. Such variations are within the scope of the invention, if they are within the tenor of the accompanying claims.

I claim:

1. Apparatus for handling loads comprising a fluidoperated hoist including a hoist chamber, a flexible member, and a piston in said chamber for raising and lowering the flexible member in response to pressure of fluid in said chamber, a load-handling unit connected to said flexible member, fluid-operated engaging means carried by said load-handling unit for engaging and disengaging a load, a hand-controlled valve remotely positioned from said fluidoperated hoist for controlling pressure of fluid in said chamber, said valve having at least two positions, the chamber pressure being at one value when said valve is in one position and the chamber pressure being at a higher value when said valve is in the other position, a manually-operated valve for supplying fluid under pressure to said fluid-operated engaging means to cause said engaging means to disengage a load carried thereby, and a pressure-responsive valve communicating with said fluid-operated engaging means and responsive to the pressure of fluid in said hoist chamber, said pressure-responsive valve being closed when said hand-operated valve is in the other position, said pressure-responsive valve, when closed, preventing operation of said fluid-operated engaging means to disengage the load even when said manuallyoperated valve is opened.

2. Apparatus according to claim I characterized further by a pilot fluid-controlled regulator and a first line connecting the regulator with said hand-controlled valve.

3. Apparatus according to claim 2 characterized by said hand-controlled valve having a third position with the chamber pressure being at a still higher value when said hand-controlled valve is in the third position, said pressure-responsive valve also being closed when said hand-controlled valve is in the third position.

4. Apparatus for handling loads comprising a fluidoperated hoist including a chamber, a flexible member, and means for raising and lowering the flexible member in response to fluid pressure in said chamber, a loadhandling unit connected to said flexible member, said unit comprising at least one vacuum cup, means for establishing a vacuum in said cup, a valve for controlling pressure of fluid in said chamber, said valve having at least two positions, the chamber pressure being at one value when said valve is in one position and the chamber pressure being at a higher value when said valve is in another position, a manually-operated valve communicating with said vacuum cup and effective to destroy the vacuum in said cup when said manually-operated valve is opened, a pressure-responsive valve interposed between said vacuum cup and said manually-operated valve to render said manually-operated valve ineffecpreventing the supply of the fluid, when closed. 

1. Apparatus for handling loads comprising a fluid-operated hoist including a hoist chamber, a flexible member, and a piston in said chamber for raising and lowering the flexible member in response to pressure of fluid in said chamber, a load-handling unit connected to said flexible member, fluid-operated engaging means carried by said load-handling unit for engaging and disengaging a load, a hand-controlled valve remotely positioned from said fluid-operated hoist for controlling pressure of fluid in said chamber, said valve having at least two positions, the chamber pressure being at one value when said valve is in one position and the chamber pressure being at a higher value when said valve is in the other position, a manually-operated Valve for supplying fluid under pressure to said fluid-operated engaging means to cause said engaging means to disengage a load carried thereby, and a pressure-responsive valve communicating with said fluid-operated engaging means and responsive to the pressure of fluid in said hoist chamber, said pressure-responsive valve being closed when said hand-operated valve is in the other position, said pressure-responsive valve, when closed, preventing operation of said fluid-operated engaging means to disengage the load even when said manually-operated valve is opened.
 2. Apparatus according to claim 1 characterized further by a pilot fluid-controlled regulator and a first line connecting the regulator with said hand-controlled valve.
 3. Apparatus according to claim 2 characterized by said hand-controlled valve having a third position with the chamber pressure being at a still higher value when said hand-controlled valve is in the third position, said pressure-responsive valve also being closed when said hand-controlled valve is in the third position.
 4. Apparatus for handling loads comprising a fluid-operated hoist including a chamber, a flexible member, and means for raising and lowering the flexible member in response to fluid pressure in said chamber, a load-handling unit connected to said flexible member, said unit comprising at least one vacuum cup, means for establishing a vacuum in said cup, a valve for controlling pressure of fluid in said chamber, said valve having at least two positions, the chamber pressure being at one value when said valve is in one position and the chamber pressure being at a higher value when said valve is in another position, a manually-operated valve communicating with said vacuum cup and effective to destroy the vacuum in said cup when said manually-operated valve is opened, a pressure-responsive valve interposed between said vacuum cup and said manually-operated valve to render said manually-operated valve ineffective when said pressure-responsive valve is closed, and means connecting said pressure-responsive valve with the hoist chamber to cause said pressure-responsive valve to close when the chamber pressure is at the higher value.
 5. Apparatus according to claim 4 characterized by said manually-operated valve including positive-pressure means for supplying fluid under positive-pressure to said vacuum cup when said manually-operated valve is open, said pressure-responsive valve preventing the supply of the fluid, when closed. 